CVE-2013-2686 in Asterisk
Summary
by MITRE
main/http.c in the HTTP server in Asterisk Open Source 1.8.x before 1.8.20.2, 10.x before 10.12.2, and 11.x before 11.2.2; Certified Asterisk 1.8.15 before 1.8.15-cert2; and Asterisk Digiumphones 10.x-digiumphones before 10.12.2-digiumphones does not properly restrict Content-Length values, which allows remote attackers to conduct stack-consumption attacks and cause a denial of service (daemon crash) via a crafted HTTP POST request. NOTE: this vulnerability exists because of an incorrect fix for CVE-2012-5976.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 12/24/2017
The vulnerability described in CVE-2013-2686 represents a critical stack consumption issue within the HTTP server component of Asterisk Open Source and Certified Asterisk distributions. This flaw specifically affects versions prior to the mentioned patches across multiple release branches including 1.8.x, 10.x, and 11.x, with the Certified Asterisk variant also impacted through version 1.8.15-cert2 and the Asterisk Digiumphones variant. The vulnerability stems from inadequate validation of Content-Length header values in HTTP POST requests, creating a pathway for remote attackers to manipulate the daemon's memory consumption patterns. This issue is particularly concerning as it was introduced as a flawed remediation for CVE-2012-5976, demonstrating how security fixes can inadvertently create new attack vectors when not thoroughly validated.
The technical implementation of this vulnerability exploits the HTTP server's failure to properly validate Content-Length values during HTTP POST request processing. When a maliciously crafted HTTP POST request is submitted with an oversized or malformed Content-Length value, the server's memory allocation mechanisms become consumed in a manner that exhausts stack space. This consumption pattern directly leads to stack overflow conditions that ultimately cause the Asterisk daemon to crash and restart, resulting in a denial of service condition. The vulnerability operates at the application layer and requires only network access to the affected HTTP server to exploit, making it particularly dangerous in production environments where continuous service availability is critical.
From an operational impact perspective, this vulnerability presents significant risks to organizations relying on Asterisk for voice over IP communications and telephony services. The denial of service condition can result in complete disruption of voice communication services, potentially affecting hundreds or thousands of users depending on the scale of the deployment. The daemon crash creates immediate service interruption that can last from minutes to hours while the system restarts and reinitializes. Security researchers have classified this vulnerability under CWE-129, which represents "Improper Validation of Array Index," as the flawed Content-Length handling essentially creates an array index validation error that leads to memory exhaustion. The vulnerability also aligns with ATT&CK technique T1499.004, which covers "Endpoint Denial of Service," specifically targeting the availability aspect of the system through resource exhaustion attacks.
The mitigation strategy for CVE-2013-2686 requires immediate deployment of patched versions across all affected Asterisk installations, including the Certified Asterisk variants and Digiumphones distributions. Organizations should prioritize updating to the specific patched versions mentioned in the CVE description, as the vulnerability was introduced as an incorrect fix for CVE-2012-5976 and represents a regression in security posture. Network administrators should also implement additional monitoring to detect unusual Content-Length header values in HTTP traffic and consider implementing rate limiting or connection throttling mechanisms as defensive measures. The vulnerability demonstrates the importance of comprehensive testing of security patches and the potential for remediation efforts to introduce new security weaknesses, particularly in complex systems like telephony platforms where multiple attack vectors exist simultaneously.